Score the pork belly skin in a diamond pattern. Turn over, poke the flesh about 12 times with a knife tip without going right through. Mix the garlic, fennel and rosemary and rub all over the belly. Season well. Wrap the belly around the pork loin, tying it at 5cm (2in) intervals with kitchen string. Rub the skin with 2 tsp fine salt, then the oil, and leave for 30 minutes.

Preheat the oven to 230°C/450°F/gas mark 8. Place the porchetta on a wire rack set over a roasting-tin and roast for 45 minutes, until the skin is puffed and golden. Lower the heat to 150°C/300°F/gas mark 2, pour boiling water to cover the bottom of the roasting-tin, cover the roast loosely with foil and cook for 2½ hours. To ensure a moist roast and a delicious gravy, check that there is a thin layer of liquid in the tin at all times.

Meanwhile make the salsa rossa. Cook the onion in olive oil for five minutes. Add the garlic and cook for a minute. Add the rest of the ingredients, season well and simmer for 45 minutes. Adjust the seasoning with sugar and vinegar during cooking. Set aside.

Remove the porchetta from the oven, wrap well with more foil and leave to rest for at least 30 minutes before carving.

Make the salsa verde at the last minute, mixing together all the ingredients, except the olive oil and lemon juice, in a bowl. Gradually stir in the oil until well blended. You might need more or less, according to your taste. Season with the lemon juice and set aside.

Slice the porchetta and serve with the lukewarm salsa rossa and salsa verde.